EFFECTS OF PRESTRAIN ON PRECIPITATION HARDENING OF CU ADDED ULTRA-LOW CARBON COLD-ROLLED STEEL SHEET

Effect of prestrain on the precipitation hardening in 1.4%Cu-added ultra-low carbon Ti-added steel has been studied. The specimens were aged at temperatures below 550-degrees-C after annealing or subsequent prestrain up to 10%. The as-annealed specimens showed considerable precipitation hardening only around 550-degrees-C. While the prestrained specimens hardened at a temperature as low as 350-degrees-C. The electrical resistivity and hardness measurements revealed that there existed a new nose for Cu aging around 400-degrees-C in addition to normal one around 600-degrees-C. The former nose can be related to formation of metastable phase, and was largely accelerated by the prestrain. This acceleration effect can be explained in terms of higher diffusivity of Cu atoms due to excess vacancies formed by the prestrain.